A double-spindle machining apparatus is known from U.S. Pat. No. 8,661,950 having a frame defining a first transfer station and a first machining station thereabove, a first spindle having a workpiece grab and vertically displaceable on the frame between an upper position with the grab in the machining station and a lower position with the grab in the transfer station, a tool holder horizontally displaceable on the frame toward and away from the machining station, and a workpiece conveyor extending through the transfer station. After shifting a deflector underneath the machining station into a side position out from underneath the grab, the grab is lowered to pick an at least partially unmachined workpiece in the transfer station off the conveyor and then raised with the workpiece into the machining station. The deflector is then shifted into a use position over the transfer station and under the machining station, and a tool held in the tool holder is engaged with the workpiece in the machining station and machining the workpiece such that chips fall from the workpiece while maintaining the deflector in the use position and deflecting the falling chips with the deflector away from the transfer station. Then the machining of the workpiece is stopped and the deflector is shifted into the side position and the grab is lowered with the machined workpiece onto the conveyor in the transfer station. Finally, the machined workpiece is transported out of the transfer station and a fresh at least partially unmachined workpiece is moved into the transfer station.
Thus the loading and unloading or transfer station is located directly underneath the machining station so that the workpiece spindle can deposit and pick up a completely finished workpiece and pick up an unfinished workpiece on the conveyor by solely moving vertically. Even though the workpiece spindle can only be moved vertically, no additional loading and unloading device is needed. With this method, a two-spindle machine tool can be operated particularly advantageously, and the tool holder or turret can be moved exclusively horizontally back and forth between the two workpiece spindles. This double-spindle machine requires only three controlled axes.
Another machining apparatus is known from U.S. Pat. No. 5,699,598 having a combined slide formed of partial slides and movable in the X direction on two linear guides by guide carriages. The two partial slides are supported directly relative to one another by support guides and can be moved in the X direction relative to one another in order to carry out a correcting adjustment or a feed movement. Each partial slide supports a vertical spindle movable in the Z direction. A joint multiple turret is associated with the vertical spindles and is provided with tools associated with the two tool spindles. The vertical spindles and the partial slides have separate drives that can be controlled by a controller such that the vertical spindles and the partial slides are displaceable jointly and synchronously or relative to one another in order to carry out a correcting adjustment or a feed movement. Due to the relative displacement of the partial slides in the X direction and the vertical spindles in the Z direction, tolerances and deviations due to wear of the cutting edges can be compensated for so that the workpieces to be machined simultaneously have the same adjustment with respect to the tool cutting edges. The relative displacement also permits a separate, varying machining of the workpieces.